Most Antminer models have dual fans for cooling. One fan sucks cool outside air in, this air passes over the chips to remove heat, and the second fan blows the air out. These are both big and fast fans which generate a lot of noise. They’re very effective at cooling the unit. Your job is to ensure that the ambient temperature in the room where the miners are housed is within its operating limits. I believe it will perform best below 25^C, but cooler is better. The hotter the air around the unit, the less cooling will be achieved by the fans. This may require you to implement some kind of ventilation unit for the room where you’re housing the S9, as a sealed room will quickly fill up with the S9’s exhaust heat.